Eat First with Your Senses: Cephalic Phase Responses

Imagine arriving at your favorite restaurant on a Friday night. 

The savory aroma welcomes you at the door and sizzling from the kitchen beckons you to your favored booth. You release the tensions of the week and sink into your seat while eyeing the menu. Each passing plate catches your eye while you contemplate your order. Is your mouth watering yet?  

The first phase of digestion, the cephalic phase, starts before you eat and primes your gastrointestinal tract for an optimal digestion experience. 

“Cephalic” refers to the head. During the cephalic phase when you think about, smell, see, taste, or anticipate food your brain jumps into action and creates a physiological response to the input from your five senses (Liddle, 2012; Lasschuijt et al, 2020). It enlists the vagus nerve, a critical part of the parasympathetic (think “rest and digest”) nervous system, to signal increases in the production of saliva, bile, stomach acid, enzymes, gastric and pancreatic hormones within minutes, and prompts gut motility (Liddle, 2012; Drossman, 2016; Lasschuijt et al, 2020). In other words, this transient but significant response to sensing or expecting food has helpful ripple effects through your whole gastrointestinal tract. 

Scientists have recognized the cephalic phase --originally called “psychic secretions”-- for over a century (Lasschuijt et al, 2020). None other than Ivan Petrovich Pavlov won the 1904 Nobel Prize in Physiology or Medicine for his experiments demonstrating the cephalic phase and its control by vagal innervation in dogs (Wood et al, 2004; Drossman et al, 2016). Needles and tubing tend to spoil our appetite, so studying the cephalic phase response in humans during real-world meals is tricky.

Prior research attempts employed sham feeding, which meant participants saw, smelled, tasted, and chewed food but did not swallow, and their cephalic phase pancreatic secretion reached 25-50% of maximal output, lasted about 60 minutes, and stopped when feeding was done, while animals experienced a longer response (Liddle, 2012). But sham feeding is not exactly a real meal. In attempted research since, there appears to be substantial variation in cephalic phase responses between individuals, especially when it comes to factors like food cues, timing, and hormone secretion, with questionable relevance to blood sugar control (Lasschuijt et al, 2020). 

Luckily, while we wait for clarifying human studies, it is free and simple to leverage the cephalic phase response to promote digestion. 

Think back to the restaurant scenario: before beginning to eat, you noticed the scent, sight, appearance, and sound of your meal and anticipated its arrival. Your senses prompt your cephalic phase response--mouthwatering is the evidence. But if you’re like me, it is easy to pay more attention to the clock than my plate and to rush through meals in mere minutes. This habit skips most sensory mealtime experiences except taste and chewing, and leaves the cephalic phase response with little time to prime the gastrointestinal tract before food arrives. 

Especially if you struggle with digestion, try prompting cephalic phase to optimize your gastrointestinal tract for digestion before meals. Here are a few free and simple ways to get started today: 

1. Participate in food preparation before your meal to prolong your sensory experience. 
2. Describe your food using as many of your five senses as you can before and during your meal. Don’t forget sight, smell, taste, touch, or sound. 
3. Act like a foodie and see if you can taste and name all the ingredients as you enjoy your first few bites at meal time. 
4. Eat slowly and chew thoroughly.
5. Minimize distractions and stress as much as possible so that you can focus on your food: avoid phones, work, computers, and TVs. 
6. Designate a place to eat and habitually use it only for meals.
7. Eat off a plate where you get to see your food, and not directly from a container. 
8. Talk to your doctor if you have loss of taste or smell or sudden changes to your senses because these can be important symptoms of serious health conditions. 

Bon appetit! 

_{Wood JD. The first nobel prize for integrated systems physiology: Ivan Petrovich Pavlov, 1904. Physiology (Bethesda). 2004;19:326-330. doi:10.1152/physiol.00034.2004}

_{Drossman DA. Functional Gastrointestinal Disorders: History, Pathophysiology, Clinical Features and Rome IV [published online ahead of print, 2016 Feb 19]. Gastroenterology. 2016;S0016-5085(16)00223-7. doi:10.1053/j.gastro.2016.02.032}

_{Lasschuijt MP, Mars M, de Graaf C, Smeets PAM. Endocrine Cephalic Phase Responses to Food Cues: A Systematic Review. Adv Nutr. 2020;11(5):1364-1383. doi:10.1093/advances/nmaa059}

_{Liddle RA. Chapter 52: Regulation of Pancreatic Secretion. In: Johnson LR, Ghishan FK, Kaunitz JD, Merchant JL, Said HM, Wood JD, eds. Physiology of the Gastrointestinal Tract. 5th ed. Academic Press; 2012:1425-1460.} 

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